This invention relates to an automatic exposure controlling type electronic photographic flash device capable of bounce flashing with satisfactory results by providing automatic light amount controlling means.
Recently, electronic photographic flash devices, i.e. strobo-flash devices have become widely used in photography for lighting the photographic object. In such automatic electronic flash devices, the lighting time of the strobo tube is automatically responsive, responding to the light reflected by the photographic object, by a controlling circuit having a photoelectric element which is directed at the photographic object to receives light reflected therefrom. With such conventional automatic type strobo flash devices, in order to control strobo tube current fed from an energy storing capacitor to the strobo tube, a switching device, for instance, a small gas discharge tube with a triggering electrode or a semiconductor switching device (thyristor), is used. The switching device stops the current of the strobo tube at a time dependent on the intensity of the reflected light. U.S. Pat. No. 3,869,642 granted Mar. 4, 1975 to Mekmet Sabanci and U.S. Pat. No. 3,779,142 which was granted to Kataro Yata Dec. 18, 1973 disclose such prior art arrangements.
Though the above-mentioned automatic type strobo flash devices have automatic light amount controlling means, in the case of bounce flash photography, wherein light from the flash is directed not to the photographic object but to a wall or ceiling, such devices are liable to cause underexposure. More particularly, when, as shown in FIG. 1, the flash light is bounced from a wall or ceiling W of, for instance, white or reflective color, the longer wavelength part or a part close to the infrared light of the flashed light is strongly reflected toward the photographic object 0. However, a considerable part of shorter wavelength or a bluish part of the flash light is scattered in all directions and therefore is not efficiently reflected toward the photographic object. As a result, the photographic object is illuminated by light which is more reddish than the original flashed light. The photoelectric element P generally used for receiving reflected light from a photographic object to measure the intensity thereof, is a photodiode or phototransistor. Such photoelectric elements have their sensitivity peak at longer wavelengths. Moreover, ordinary photographic film has a sensitivity spectrum similar to that of human eyes and has substantially no sensitivity in the infrared range. Accordingly, in the case of bounce flashing, the photoelectric element P of such conventional flash devices produces sufficient electric output, but the film of the camera receives less light then with ordinary flashing. Therefore, the picture thus take is underexposed.
Next, as shown in FIG. 2, when the bounced light illuminates a wall W' which is behind the photographic object, in addition to the reason described referring to FIG. 1, the light reflected by the back wall, W', over the area covered by the solid incident angle .theta. to the photoelectric element P, also strikes the photoelectric element P. Accordingly, the flash device stops its flash even faster than in the case of FIG. 1, and hence the resultant picture is further underexposed. When other reflective things exist behind or to the side of the photographic object, the degree of the underexposure becomes still greater.
Several devices have been made to rotate a reflector associted with the flash tube or to move slide-in shoe of the flash unit case in order to direct flash light toward a ceiling or a wall for bounce flashing. (for instance, U.S. Pat. No. 3,869,604, issued on Mar. 4, 1975Prochnow to Claus). However such devices have required complex rotating parts in the case, and hence have increased the size of the case. Such increased case size is not desirable in a miniaturized flash device.